In the manufacture of high-density information records, a diamond cutterhead assembly is used to cut a surface relief pattern, including information bits and tracking aids, into a metallic recording substrate. The cutterhead assembly includes a diamond stylus, a piezoelectric element and a pedestal member which is attached to a mounting bracket by means of a damping material.
As disclosed in U.S. Pat. No. 4,035,590 to Halter, herein incorporated by reference, damping is provided by a rigid member made, for example, of Kapton, a plastic available from the DuPont Company, and one or more pliable layers contacting the rigid member which are made of a silicone rubber or a cellulosic material such as Viscoloid, available from American Viscose Company. This structure serves to attenuate and therefore inhibit reflection of the propagating waves generated by the piezoelectric element and also serves to de-couple the moving portion of the cutterhead from the resonant modes within the cutterhead assembly support.
The above cutterhead assembly has been successfully used to cut recording substrates at one-half real time, that is, the recording is made at one-half the speed at which the record will be played back. Since recording at real time rates obviously represents a major saving in recording time and would result in substantial cost savings for manufacturing records, attempts have been made to record at real time. Recording at real time increases the speed of cutting and therefore the temperatures generated during recording. The heat which is transmitted to the cutterhead assembly is greatly increased, with temperatures being generated up to 150.degree. C. or even higher.
The damping materials used heretofore are inadequate at such high temperatures. Viscoloid, for example, is a solvent-based material that melts at such temperatures and thus is dimensionally unstable for real time recording. Other materials that have been tried, such as commercially available epoxy resins cured at room temperature, which when exposed to the higher temperatures, continue to cross-link thereby changing the damping character of the materials over a wide temperature range.
Other stringent criteria exist for a good damping material for this application. In addition to dimensional and damping stability at elevated temperatures, the damping material must be flexible over a whole range of temperatures from room temperature to over 150.degree. C. Another criteria is that the material be flexible, i.e., have a T.sub.g, below room temperature. In addition, the material must be able to damp over a wide range of temperatures and thus must have a high thermal conductivity, because at the same time that the air-material interface is at room temperature, the material-piezoelectric interface may be as high as about 150.degree. C. Also the material must be stable with respect to time as well as to temperature.
Thus since real time recording would result in a substantial cost savings, a search for a damping material effective and stable over a wide range of temperatures has continued.